The present disclosure relates to two-component developer.
In general, in electrophotography, after the surface of a photosensitive drum is electrostatically charged by corona charging or the like, exposure using a laser or the like is performed to form an electrostatic latent image. Then, the formed electrostatic latent image is developed with toner to form a toner image. Further, the formed toner image is transferred to a recording medium, thereby obtaining a high-quality image. In forming the toner image, toner particles (toner base particles) with an average particle diameter of 5 μm or larger and 10 μm or smaller are used usually. Such toner base particles can be obtained through mixing of binder resin, such as thermoplastic resin with colorant, a charge control agent, a releasing agent, etc., kneading, pulverization, and classification. Further, in order to provide fluidity and suitable electrostatic charging characteristics to the toner and to enhance the ability to clean the toner from the photosensitive drum, inorganic particulates of silica, titanium oxide, or the like are externally added to the toner base particles.
As development processes using the toner, there are known one-component development process using the toner solely as developer (one-component developer) and tow-component development process using developer obtained by mixing the toner and a carrier (two-component developer). In the two-component development process using the two-component developer, the carrier charges the toner by frictional charging and plays a role in toner conveyance. For this reason, the two-component development process has an advantage that charging characteristics and conveyability of the toner can be relatively stable in the beginning of image formation.
For the two-component developer used in the two-component development process, a carrier is used of which carrier core is covered with a coating layer formed with a coating agent, such as acrylic resin, silicone-based resin, and epoxy-based resin. However, where high coverage rate printing using two-component developer including such a carrier is performed for a long period of time, an external additive (external additive attached to toner surface or external additive separated from toner) and the carrier may abrade each other in a development device to cause the coating layer that covers the carrier core to peel off and to cause the external additive separated from the toner to adhere to the surface of the coating layer. Peeling off of the coating layer or adhesion of the external additive may lead to impairment of the power of the carrier for toner charge. Accordingly, fogging may tend to be caused in image formation using the above two-component developer.
In view of the forgoing, two-component developer has been proposed which uses a carrier covered with resin including polyamide-imide resin for the purpose of preventing the coating layer from peeling off from the carrier core. In addition, two-component developer has been proposed which includes a carrier with a coating layer to which fluororesin is added for the purpose of preventing the external additive separated from the toner from adhering to the surface of the carrier.